Warning: New players reading this page may be very confused.

Basic info to know:

  • Stat caps at every rarity are not a hard cap, but rather a growth cap.
    • For example: Str on a hypothetical unit does not simply reach a hardcoded value of 80 and stop; str grows by a set amount that might make its final capped value stop at 79, 80, or even 81. That they capped at different levels only means that str grew by the maximum allowed value at that rarity.
  • Typing essentially modifies probability of each stat to grow on level up, growth ceiling for all stats, and maximum stats obtainable through fusion.
  • On the global server, luck works like any other stat except when it comes to fusion cap. (Mostly irrelevant to the evolution mechanics we discuss here)
  • Evolving a unit to its next rarity allows ~10% of its stats to carry over; thresholds for stat carryover start at X1 and end at Y0, where X is any number, and Y is 1 greater than X (X1 and Y0 might be 41 and 50, or 91 and 100)
    • Thanks to /u/Kuniai (and /u/Horizonset for an important correction) because I can’t explain things in a non-dumb way: "Evolving a unit will carry over 10% of its stats within a tiered amount. All tiers start on a 1 and end in a 0, so 41-50 is 5, 51-60 is 6, etc etc.” - /u/Kuniai
    • For example: A lv50 3 star unit with 40 str will only carry 4 str into its 4 star version; however, if it had 41 str, the unit would carry 5 str over to the next evolution
  • Stats used to calculate evolution bonuses are the sum total of base stats (including previous evolution bonuses) + level up stats + fusion stats.
  • Evolution bonuses carry over to the next rarity as base stats.
  • Evolution bonuses can be transferred between units with the same art and rarity. This process takes place during regular fusion, but does not appear in the fusion preview.

There are a few important logical conclusions we can make based on this information.

  • An upper limit for evolution bonuses exists for all stats. We know this because units cannot carry over stats that would be impossible for them to achieve. If a 3 star unit has 8 base str, and can grow by 30 str max at that rarity, and can gain 5 str from fusion, the maximum possible str that unit could have is 8+30+5 = 43. This means the unit can never reach the next bonus threshold at 51, and thus cannot carry over 5 str to the next evolution. In other words, upper limits for evolution bonuses are essentially defined by the typing of the unit.
  • Evolution bonuses can be transferred until the point that the base unit cannot gain more evolution bonuses as per the above. 
  • Maximum evolution bonuses are the most important aspects of the unit that typing affects. With any given unit, different instances of that unit will have exactly the same upper limits of stat growth. The only way to make units more powerful is to modify their base stats, which are identical otherwise. The only extant way to modify a unit’s base stats is to maximize evolution bonuses.